Preparation of esters of methacrylic acid



Patented Dec. 26, 1939 PREPARATION OF ESTERS OF METHAw CRYLIC ACID Herman A. Bruson, and Robert N. Washburne,

Philadelphia, Pa., assignors to Rn'ihm Company,. Philadelphia, Pa.

No Drawing. Application July 13, 193i.

Serial No. 153,358

Claims.

This invention relates to a catalytic process for the preparation of esters of methacrylic acid from the corresponding esters of a-hydroxy-isojbutyric acid.

It has been found that under the proper conditions of temperature, space velocity and presence or absence of diluents certain catalysts will bring about the dehydration of esters of a-hydroxy-isobutyric acid in the vapor phase and yield the corresponding ester of methacrylic acid.

Many dehydrating catalysts can be used for the purpose of thisinvention. Among those useful may be mentioned thoria, silica gel, activated alumina, basic aluminum sulfate, metaor ortho-phosphoric acid supported on diatomaceous earth or graphite, and various combinations of aluminum and phosphoric acid.

The catalysts which are most eifective for this purpoze are principally those which contain aluminumoxide in combination with phosphoric acid. Part of the aluminum, up to about 50% on a molecular weight basis, may be replaced by manganese or magnesium.

These catalysts are effective at temperatures of about 325 C. to 425 C. Besides the direct dehydration of the a-hydroxy-isobutyric acid ester to methacrylic acid ester, there are side reactions taking place which yield undesirable products, usually being gaseous or having a low boiling point. At temperatures above 425 C. the amount of these undesirable by-products which are formed may become excessive and below 325 the reaction is very slow. In both cases the yield is considerably lower than that obtained within the above temperature range.

methacrylic acid ester is normal. The expression space velocity means the total volume of vapor measured in cubic centimeters at 760 mm. at 0 C. which pass per cubic ceritimeter of catalyst per hour. A decrease in the time of contact between the a-hYdlOXY-iSOblltYriC acid ester and the isobutyric acid ester decomposed. The total result, however, is a decrease in the actual yield of the methacrylic acid ester. 0n increasing the temperature to 425 a more complete decomposi- The efiect of the space velocity on the yield of change the yield of the methacrylic acid ester calculated on,the total amount of a-hydroxy-.

tion of the a-hydroxy-isobut !ric acid ester is obtained but the total yield" of the'methacry'lic acid ester is poor. -The increase in temperature causes an increase-in the amount of secondary decomposition and naturally reduces the yield of the methacrylic acid ester.

It has also been found advantageous to use diluents such as water, alcohol, benzine, etc. It is apparent that water has a specific effect on the reaction because benzol and alcohol had a tendency to decrease the yield, also "to decrease the total decomposition of the a-hydroxy-isobutyric acid ester. The effect of the water also changes somewhat with the temperature at which the reaction is carried out. Using a contact material which requires a temperature of 400 (3., water is beneficial, whereas at 375 C. theeifect is somewhat less apparent. It is possible that water may prevent too great a rehydration of the contact material at the higher temperature. Good results have been obtained when the molar ratio of water to the ester is about 2:1.

The process is carried out in general by vaporizing the ester of a-hYdIOXY-lSOblltYIiC acid, adding the proper amountof water vapor and passing the mixture over a heated catalyst at the desired temperature. The resulting. products are condensed and fractionally distilled to obtain the pure methacrylic acid ester.

The process may be illustrated by the following examples:

1. A catalyst is prepared by mixing ammonium phosphate with freshly precipitated aluminum hydroxide. 400 g. of A1(NO3)3'9H2O is dissolved in 2.5 liters of water and precipitated at with ammonium hydroxide. The precipitate is filtered immediately, washed twice with 200 cc. of water and the cake pressed. This cake is then mixed in a mortar with 324 g. of diammonium phosphate and the paste dried over a steam bath and in an oven at The dried material is then broken and placed in a converter tube at 200 to 220 C. Air is passed through the tube, the temyelocity of 234. The yield-oi ethyl methacrylate s. A mixture of 228 g. of ethyl-a-hydroxy-lsobutyrate and 62.1 ggoi water ispassed through the same catalyst at 375 C. and a space velocity of 630. The yield of ethyl'methacrylate is 54%. A 8. A mixture of 214.0 g. of ethyl-a-hydroxyisobutyrate and 58.0 g. of water is passed through the same catalyst at 400 and a space velocity of 545. The yield of ethyl methacrylate is 41%.

7. 149 g. of ethyl-a-hydroxy-isobutyrate is 1 passed through the same catalyst at 400 and a space velocity of 253. acrylate is 12%.

8. A mixture of The yield of ethyl meth- 140 g. of methyl-a-hydroxyisobutyrate and 47 g. of water is passed through the same catalyst at 375 and a, space velocity of 722. The yield is 50% of methyl methacrylate. 9. A mixture 01399 g. of methyl-a-hydroxyisobutyrate and 33 g. of water is passed through the same catalyst at- 375 and a space velocity of 553. The yield of methyl methacrylate is 49%.

10. Another catalyst of similar composition is made by mixing one mol oi ireshly precipitated aluminum hydroxide with two mols of phosphoric acid and Heating the transparent, syrupy mass until it sets to a hard, granular mass, presumably AlPO4 and polymerized HaPO4.

A mixture or 115.5 g.'of ethyl- -hydroxy-ism butyrate and 31.3 g. of water is passed over this catalyst at 375 and a space velocity of 662. The yield of ethyl methacrylate is 74%.

11. Another catalyst made in exactly the same manner as described in Example 10 is prepared.

A mixture of 121.5 g. of ethyl-a-hydroxy-isobutyrate and 33.0 g. of water is passed over this catalyst at 375 C. and The yield of ethyl methacrylate is 57%.

12. Another catalyst is made the same as that shown in Example 1 except that one-half of the aluminum is replaced by magnesium calculated on the molecular weight basis.

A'mixture 01 131.9 g. of GthYI-uz-hYdlOXY-ISO- butyrate and 36.1 g. of water is passed over this catalyst at 375 and a space velocity of 553. A yield of ethyl methacrylate of 54% is obtained.

13. A mixture of 134.6 g. of ethyl-hydroxyisobutyrate and 36.9 g. of water is passed over the catalyst described in Example 12 at 375 and a space velocity of 1085. A yield of ethyl-methacrylate of 27% is obtained.

14. A mixture of 134.8 g. of ethyl-e-hydroxyisobutyrate and 36.5 g. of water is passed over the same catalyst at 375 and a space velocity 01' 293. A yield of ethyl methacrylate of 37% is obtained.

15. Another catalyst is made up the same as that shown in Example 12 replacing the magnesium with manganese in the same proportion.

A mixture of 130.9 g. of ethyl-e-hydroxy-isobutyrate and 35.6 g. of water is passed over this catalyst at 375 and a space velocity of 547. The yield of ethylmethacrylate is 58%.

16. A mixture of 123.7 g, of ethyl-a-hydroxyisobutyrate and 33.1 g. 01' water is passed over this a space velocity of 560.

enemas I same catalyst at 375 and a space velocity of 557. I

The yield of ethyl methacrylate is 53%.

11. A mixture oi 117.9 g. of ethyl-e-hydroxy isobutyrate and 64.9 g. of water (4 mols oi water to one oi ester) is passed over the same catalyst at 375and a space velocity of 748. 'Theyield of ethyl methacrylate is 59%.

18. A mixture of 127.6 g. or ethyi-e-hydroxyisobutyrate and 34.6 g. of water is passed over the same catalyst at 375 and a space velocity of 560.

s The yield oi ethyl methacrylate is 67%.

In the foregoing examples the, catalytic dehydration of methyl and ethyl a-hydroxy-isobutyrates has been described. The process. however, may also be applied to the e-hydroxy-isobutyric acid esters of other primary alkyl alcohols such as the n-propyl, n-butyl, n-amyl, isobutyl, iso-amyl and the higher. normal or branched-chain primary alcohols. It is not generally applicable to esters of secondary or tertiary alcohols on account of the excessive extent of side reactions which give undesirable by-products.

. We claim: Y

a l. A process for converting an ester of e-hydroxy-isobutyric acid to the corresponding ester of methacrylic acid which comprises passing the vapor of the a-hydroxy-isobutyric acid ester in contact with a dehydrating catalyst at a temperature of from about 325 C. to about 425 C.

2. A process for converting an ester of e-hy-' droxy-isobutyric acid to the corresponding ester 01' methacrylic acid which comprises passing a mixture of the vapor of the a-hydroxy-isobutyric acid ester-and a diluent in contact with a dehydrating catalyst at a temperature of from about 325 C. to about 425 C.

3. A processior converting an ester oi a-hydroxy-isobutyric acid to the corresponding ester of methacrylic acid which comprises passing a mixture of the vapors of the a-hydlOXy-lSOblltyflc acidester and water in contact with a dehydrating catalystat a temperature of from about 325 C. to about 425 C.

4. A process for preparing ethyl methacrylate which comprises dehydrating ethyl-e-hydroxyisobutyrate by passing its vapor over a dehydrating catalyst at a temperature of from about 325 C. to about 425 C.

5'. A process for preparing methyl methacrylate which comprises dehydrating methyl-e-hydroxyisobutyrate by passing its vapor over a dehydrating catalyst at a temperature of from about 325 C. to about 425 C.

'6. A process for preparing ethyl methacrylate which comprises dehydrating ethyl-a-hydroxyisobutyrate by passing a mixture of the vapors oi ethyl-e-hydroxy-isobutyrate and water in contact with a dehydrating catalyst at a temperature of from about 325 C. to about 425 C.

7. A process for preparing methyl methacrylate which comprises dehydrating methyl-a-hydroxyisobutyrate by passing a mixture of the vapors oi methyl-a-hydroxy-isobutyrate and water in contact with a dehydrating catalyst at a temperature of from about 325 C. to about 425 C.

8. The process for converting an ester of athydroxy-isobutyric acid to the corresponding ester oi. methacrylic acid which comprises passing the vapor oi the u-hydroxy-iscbutyric acid ester in contact with a dehydrating catalyst containing a phosphate of aluminum at a temperature from about 325 C. to about 425 C.

9. The process for converting an ester of uhydroxy-isobutyric acid to the corresponding ester of methacrylic acid which comprises passing a-mixture or the vapor of the a-hydroxy-isobutyric acid ester and a diluent in contact with a dehydrating catalyst containing a phosphate of aluminum at a temperature or from about 325 C. to about 425 C.

10. The process for preparing ethyl methacrylate which comprises dehydrating ethyl-ahydroxy-isobutyrate by passing a mixture of the vapors of ethyl-a-hydroxy-isobutyrate and water in contact with a dehydrating catalyst containing a phosphate of aluminumat a temperature of from about 325 C. to about 425 C.

11. The process for preparing methyl methacrylate which comprises dehydrating methyl-ahydroxy-isobutyrate by passing a mixture of the vapors of methyl-a-hydroxy-isobutyrate and water in contact with a dehydrating catalyst containing a phosphate of aluminum at a tem perature of from about 325 C. to about 425 C;

12. The process for converting an ester or ahydroxy-isobutyric acid to the corresponding ester of methacrylic acid which comprises passing the vapor or the a-hydroxy-isobutyric acid ester in contact with a dehydrating catalyst containing a mixture oi a phosphate of aluminum and one of the group consisting of phosphates of manganese and magnesium at a temperature or from about 325 C. to about425 C. L

13. The process for converting an ester of ahydroxy-isobutyric' acid to the corresponding ester of methacrylic acid which comprises passing a mixture oi. the vapor or the u-liYdl'OXY-ISO- butyric acid ester and a diluent in contact with a dehydrating catalyst containing a mixture of a phosphate of aluminurnand one of the group consisting of phosphates of manganese and magn'esium at a temperature of from about 325 C. to about 425 C.

14. The process for preparing ethyl methacrylate which comprises dehydrating ethyl-ahydroxy-isobutyrate by passing a mixture of the .vapors of ethyl-a-hydroxy-isobutyrate and water in contact with a dehydrating catalyst containing a mixture of a phosphate 01 aluminum and one of the group consisting of phosphates of manganese and magnesium at a temperature qt from about 325 C. to about 425 C.

15. The..process for preparing methyl metha- -,crylate which comprises dehydrating methyl-at' iflxwisobutyrate by passing a mixture of the vapors io'r methyl-a-hydroxy-isobutyrate and 

